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Chapter 2
Neuroscience and Behavior
Neurons and Synapses
Types of Neurons
Sensory Motor Interneurons
SpinalCord
BrainSensoryNeuron
Sensory Neurons
• INPUT From sensory organs to the brain and spinal cord
Drawing shows a somatic neuron
Motor Neurons
• OUTPUT From the brain and spinal cord to the muscles and glands
SpinalCord
BrainSensoryNeuron
MotorNeuron
SpinalCord
BrainSensoryNeuron
MotorNeuron
Interneurons
• Interneurons carry information between other neurons only found in the brain and spinal cord
Parts of a Neuron
The Cell Body
– round, centrally located structure – contains DNA– controls protein manufacturing – directs metabolism– no role in neural signaling
Contains the cell’s nucleus
Dendrites
• Information collectors
• Receive inputs from neighboring neurons
• Inputs may number in thousands
• If enough inputs, the cell’s AXON may generate an output
Dendritic Growth
• Mature neurons generally can’t divide • But new dendrites can grow• Provides room for more connections to other
neurons• New connections are basis for learning
Axon
• The cell’s output structure
• One axon per cell, 2 distinct parts– tube-like structure – branches at end that connect to dendrites
of other cells
Myelin Sheath
• White fatty casing on axon • Acts as an electrical insulator • Not present on all cells• When present, increases the speed of neural
signals down the axon
How Neurons Communicate
• Neurons communicate by means of an electrical signal called the action potential.
• Action potentials are based on movements of ions between the outside and inside of the cell.
• When an action potential occurs, a molecular message is sent to neighboring neurons.
Action Potential Within a Neuron
Resting Potential
• At rest, the inside of the cell is at -70 microvolts.• With inputs to dendrites, the inside becomes more positive. • If resting potential rises above threshold, an action potential
starts to travel from cell body down the axon.• Figure shows resting axon being approached by an AP.
Depolarization Ahead of AP
• AP opens cell membrane to allow sodium (Na+) to enter.
• Inside of cell rapidly becomes more positive than outside.
• This depolarization travels down the axon as leading edge of the AP.
Repolarization follows
• After depolarization, potassium (K+) moves out restoring the inside to a negative voltage.
• This step is called repolarization.• The rapid depolarization and repolarization produce a
pattern called a spike discharge.
Finally, Hyperpolarization
• Repolarization leads to a voltage below the resting potential, called hyperpolarization.
• Now, the neuron cannot produce a new action potential.• This is the refractory period.
Neuron to Neuron
• Axons branch out and end near dendrites of neighboring cells.
• Axon terminals are the tips of the axon’s branches.
• A gap separates the axon terminals from dendrites.
• The gap is called the synapse.
Neurotransmitter Release
• Action potential causes vesicle to open.
• Neurotransmitter released into synapse.
• Neurotransmitter locks onto receptor molecule in postsynaptic membrane.
Excitatory and Inhibitory Messages
• Excitatory message — increases the likelihood that the postsynaptic neuron will activate
• Inhibitory message — decreases the likelihood that the postsynaptic neuron will activate.
Locks and Keys
• Neurotransmitter molecules have specific shapes.
• When NT binds to receptor, ions enter.
• Receptor molecules have binding sites.
Some Drugs Work on Receptors
• Some drugs are shaped like neurotransmitters.
• Antagonists: fit the receptor but poorly and block the NT– e.g., beta blockers
• Agonists: fit receptor well and act like the NT– e.g., nicotine
Types of Neurotransmitters
• Acetylcholine
• Dopamine
• Serotonin
• Norepinephrine
• GABA
• Endorphins
Acetylcholine (Ach)
• Found in neuromuscular junctions• Involved in muscle movements• Involved in learning and memory
Disruption of Acetylcholine Functioning
• Curare — blocks ACh receptors– paralysis results
• Nerve gases and Black Widow spider venom — too much ACh leads to severe muscle spasms and possible death
Disruptions in ACh Functioning
• Cigarettes — nicotine works on ACh receptors– can artificially stimulate skeletal
muscles, leading to slight trembling movements
Alzheimer’s Disease
• Deterioration of memory, reasoning, and language skills
• Symptoms may be due to loss of ACh neurons
Dopamine
• Involved in movement, attention, and learning
• Dopamine imbalance also involved in schizophrenia
• Loss of dopamine-producing neurons is cause of Parkinson’s disease
Parkinson’s Disease
• Results from loss of dopamine-producing neurons in the substantia nigra
• Symptoms include– difficulty starting and stopping voluntary movements– tremors at rest– stooped posture– rigidity– poor balance
Parkinson’s Disease
• Treatments– L-dopa– transplants of fetal dopamine-producing
substantia nigra cells– adrenal gland transplants– electrical stimulation of the thalamus has
been used to stop tremors
Serotonin
• Involved in sleep
• Involved in depression– Prozac works by keeping serotonin in
the synapse longer, giving it more time
to exert an effect
Norepinephrine
• Arousal
• “Fight or flight” response
Endorphins
• Control pain and pleasure
• Released in response to pain
• Morphine and codeine work on endorphin receptors; involved in healing effects of acupuncture
• Runner’s high— feeling of pleasure after a long run is due to heavy endorphin release
GABA
• Inhibition of brain activity
• Huntington’s disease involves loss of neurons in striatum that utilize GABA– Symptoms:
• jerky involuntary movements• mental deterioration
Summary
• Neuron structure• Action potentials• Synapse• Neurotransmitters• Receptors and ions• Agonists and
antagonists
Parts of the Nervous System
• Central Nervous System (CNS)– Brain and spinal cord
• Peripheral Nervous System (PNS)– Carries messages to and from CNS
Central nervous system
Peripheral nervous system
Sympathetic and parasympathetic divisions of the nervous system
Endocrine System
• Pituitary gland — attached to the base of the brain, hormones affect the function of other glands
• Adrenal glands — hormones involved in human stress response
• Gonads — hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females.
Brain
• Images
• Brainstem– Hindbrain– Midbrain
• Forebrain– Limbic system– Cortex
Developing Brain
•Neural tube — beginning of nervous system develops at 2 weeks after conception
•Neurogenesis — development of new neurons
Hindbrain Structures
• Cerebellum
• Brainstem– medulla– reticular
formation– pons
Cerebellum• Coordinated, rapid
voluntary movements– e.g., playing the
piano, kicking, throwing, etc.
• Lesions to cerebellum– jerky, exaggerated
movements
– difficulty walking
– loss of balance
– shaking hands
Medulla
• Breathing• Heart rate• Digestion• Other vital
reflexes– swallowing– coughing– vomiting– sneezing
Reticular Formation
• Network of neurons in the brainstem (and thalamus)
• Sleep and arousal
• Attention
Pons• Helps coordinate movements on left and right sides of the body– e.g., postural
reflexes which help you maintain balance while standing or moving
Forebrain Structures
• Thalamus
• Limbic System
• Cortex
Thalamus
• Relay station in brain• Processes most
information to and from higher brain centers
The Limbic System
• Hypothalamus
• Amygdala
• Hippocampus
Hypothalamus
• Contains nuclei involved in a variety of behaviors– sexual behavior– hunger, thirst– sleep– water and salt balance– body temperature regulation– circadian rhythms– role in hormone secretion
Hypothalamus and Hormones
Hypothalamus releases hormones or releasing factors which in turn cause pituitary gland to release its hormones
Amygdala and Emotion
• Identify emotion from facial expressions
Amygdala damage makes this task difficult
(click on picture to advance photos)
Cortical Specialization
• Localization — notion that different functions are located in different areas of the brain
• Lateralization — notion that different functions are processed primarily on one side of the brain or the other
Lobes of the Cortex• Frontal lobe — largest lobe, produces
voluntary muscle movements, involved in thinking, planning, emotional control
• Temporal lobe — primary receiving area for auditory information
• Occipital lobe — primary receiving area for visual information
• Parietal lobe — processes somatic information
Language and the Brain
• Aphasia — partial or complete inability to articulate ideas or understand language because of brain injury or damage
• Broca’s area — plays role in speech production
• Wernike’s area — plays role in plays role in understanding and meaningful speech
Split brain operation—procedure used to reduces recurrent seizures of severe epilepsy
Corpus callosum—thick band of axons that connects the two cerebral hemispheres